1. Field of the Invention
The present invention relates to a golf club, and in particular to the construction of the head of an iron club.
2. Description of the Related Art
As a head for an iron club there is the so called cavity back type head. The cavity back type head is one where a cavity comprising a hollow portion is formed in the rear of a head body having a face, being the striking face, on the front thereof. In this way, the face can be widened without increasing the weight of the head body, and also the inertia moment of the head can be increased by distributing the weight to the peripheral portion away from the face, thus enabling further widening of the sweet area. That is to say, even when the ball is hit at a position away from the foot of a perpendicular line from the face to the center of gravity of the head, deflection of the head is minimal, thereby reducing mis-shots.
With the cavity back type head however, rigidity is poor compared to the so called muscle type head which has no cavity. There is thus the problem that the face is susceptible to distortion particularly when the ball is hit at a location away from the sweet spot, thus giving rise to deviation in the direction of flight of the ball. Furthermore there is the problem, particularly when the cavity is formed by machining, that cutter marks from the tool remain, impairing the attractiveness. Conventionally, in order to make the cutter marks less conspicuous, shot blasting is carried out, however there is a limit to this.
Furthermore, for example as disclosed in Japanese Unexamined Utility Model Publication No. 60-97158, in order to adjust the weight balance, a weight made from a denser material than that of the head body, is positioned inside the cavity of the head body. However, this results in limitations to the method of attachment and the design to ensure that the attractiveness is not impaired by the externally exposed weight, thus posing difficulties to the free selection of materials and balance adjustment. Furthermore, while for the materials which can be used for the weight itself, there are also those with poor corrosion resistance (for example copper or beryllium copper or tungsten) or with poor strength (for example lead), since low corrosion resistance and strength can also be the cause of a loss in attractiveness, then from this point also there is a limit to the material which can be used as the weight.
In Japanese Unexamined Patent Publication No. 62-201168, there is disclosed a head for an iron club where, in order to increase the natural frequency of the base surface portion of the head to extend the flight distance of a ball, a cover (weight) made of a denser material than that of the head body is provided on the rear portion of a head body having a cavity (hollow portion) to cover the cavity, the hollow portion thus being defined by the cover and the inner face of the cavity. With this head, the cover is secured to the head body by fitting the cover into a spot facing in the head body and then bonding. However, securing using bonding results in an unreliable attachment, so that due to impact or the like during use, the cover is likely to come off from the head body.
Welding has also been considered as a means for securing the cover to the head body. However, with welding, weld marks and pin holes remain, with a loss in attractiveness. Moreover, there is also the case where, due to the material for the head body and the cover, welding is not possible. Hence there is a limit to the selection of the material. Furthermore, in the case of plating, adherence of the plating may be compromised depending on the metal material.